Mitotic spindle positioning and nuclear migration are critical for determining the size, position and developmental fate of daughter cells, and ensuring faithful segregation of the genetic material. Spindle positioning is mediated by the activity of the minus end-directed motor, dynein. Dynein is required for a variety of fundamental cellular processes, including chromosome segregation and spindle orientation during cell division. Failures of these processes can lead to aneuploidy, which is a hallmark of human cancer. To correctly position the mitotic spindle, dynein function is tightly regulated both spatially and temporally. During anaphase, dynein is targeted to, and anchored at the cell cortex, where its motor activity mediates spindle positioning. The mechanism by which dynein activity is regulated is not known, however, in yeast, a cortical anchor - Num1 - has been identified. OBJECTIVE/SPECIFIC AIMS: My goal is to fully characterize the spatial and temporal regulation of dynein. To answer this fundamental question, I will examine the regulation of dynein by its cortical anchor, Num1. I will examine Num1 transit during anaphase and identify the components required for this process. I will determine oligomeric state of Num1 and identify the subunit of dynein that interacts with Num1 in vitro. Finally, I will determine the Num1 domain responsible for oligomerization and dynein interaction. Understanding the exact nature of the interaction between dynein and its cortical anchor, as well as the regulation of that anchor, will progress our understanding of the basic biological process of spindle positioning, and related human disease.